1. Field of the Invention
The present invention relates generally to a combustion heater for an internal combustion engine and, more particularly, to a combustion heater for an internal combustion engine, which is disposed in an intake passageway of the internal combustion engine and raises temperature of engine related elements.
2. Description of the Prior Art
An internal combustion engine requires speeding up both a start and a warm-up thereof at a cold time. For example, Japanese Patent Application Laid-Open Publication No.62-75069 discloses an art of warming the engine cooling water by utilizing the combustion heat emitted from a vaporization type combustion heater attached to an intake passageway of the internal combustion engine, and thereby enhancing a heater performance of a car room heater as well as speeding up the warm-up of the engine.
According to this prior art, the combustion heater is operated before starting up the internal combustion engine, and the operation of the combustion heater continues for a short period of time after the engine start, thereby trying to enhance a starting characteristic of the internal combustion engine as well as speeding up the warm-up thereof.
In the prior art disclosed in the above Publication, a combustion chamber of the combustion heater includes an intake duct and an exhaust duct both of which are intake duct and an exhaust duct both of which are connected to an intake pipe of the internal combustion engine, and the air flowing through the intake pipe flows via a route of the intake pipe.fwdarw.the intake duct.fwdarw.the combustion chamber.fwdarw.the exhaust duct.fwdarw.the intake pipe, and at its halfway supplies the air as combustion air to the combustion heater. Further, an opening/closing valve defined as an intake air resisting structure is disposed at a portion of the intake pipe between respective connecting points for connecting the intake duct and the exhaust duct to the intake pipe.
As it is well known, in the internal combustion engine, a pressure and an air flow rate in the intake system change depending on a rotational speed of the engine body. Therefore, with the combustion heater disclosed in the above publication, the flow rate of the air supplied to the combustion chamber via the intake duct from the intake pipe becomes excessively large or small depending on the rotational speed of the internal combustion engine. Then, the problem of the prior art disclosed in the above Publication is that the air flow rate becomes excessively large due to the higher rotational speed of the internal combustion engine. The reason is that the excessively large air flow rate implies a state which is the same as a phenomenon of a strong air blown into the combustion chamber from the intake duct, and an air/fuel ratio becomes lean to deteriorate an ignition in the combustion heater.
On the other hand, in the case of providing the intake system with the combustion heater by setting the intake and exhaust ducts proximal to each other on the intake pipe without having the opening/closing valve disposed in the intake pipe, a differential pressure between the intake duct and the exhaust duct is small, and, even when the internal combustion engine is at a high rotational speed, the excessively large flow rate does not occur in the combustion chamber of the combustion heater. Consequently, the ignition characteristic of the combustion heater is not bad. However, when at the high rotational speed, the pressure in the intake system decreases. Hence, an air density decreases, and the air/fuel ratio in the combustion chamber becomes rich, with the result that soot is easily produced on the combustion heater. This might lead to a possibility of deteriorating the burning characteristic of the combustion heater.